1. Field of the Invention
The present invention relates to a driving device for use in small office automation equipment or the like, and in particular to a driving pulley for a steel belt.
2. Related Background Art
For office automation equipment there is desired a compact and light pulley, in consideration of dimension of the equipment. For this reason there have been employed pulleys made of light metals. Also for driving such pulley there has been employed a steel belt for preventing elongation by fatigue, since a twisted wire belt or a rubber belt results in an elongation after prolonged use, thus deteriorating the precision of belt position.
The surface of such pulley should have a high hardness in order to increase the abrasion resistance. For this purpose, there is already proposed a pulley having a thin film of a hard metal on the belt driving surface, as disclosed in the Japanese Utility Model Laid-open No. 29148/1972.However such pulley tends to show a small friction resistance, in engagement with a mirror-finished steel belt, thus eventually resulting in slippage.
Also the Japanese Patent Publication No. 44684/l982 disclosed a process of mechanically finishing the surface of an aluminum pulley and depositing a suitable amount of an extremely hard material such as chromium oxide, alumina, tungsten or tungsten carbide on said surface by melt spraying, thereby obtaining a high hardness and a high friction on said surface.
However such forced spraying of chromium oxide, alumina etc. on the surface of pulley inevitably leads to an inexact external diameter of the pulley, and such uneven dimensional accuracy gives rise to defective frictional drive for the steel belt.